linux-kernel - Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

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Date:	Mon, 11 Jan 2010 21:54:13 -0500
From:	Valdis.Kletnieks@...edu
To:	Pavel Machek <pavel@....cz>
Cc:	Michael Stone <michael@...top.org>,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-security-module@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>, David Lang <david@...g.hm>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Bryan Donlan <bdonlan@...il.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	"C. Scott Ananian" <cscott@...ott.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Bernie Innocenti <bernie@...ewiz.org>,
	Mark Seaborn <mrs@...hic-beasts.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Samir Bellabes <sam@...ack.fr>,
	Casey Schaufler <casey@...aufler-ca.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH 2/3] Security: Implement disablenetwork semantics. (v4)

On Sun, 10 Jan 2010 22:58:48 +0100, Pavel Machek said:

> Scenario 2:
> 
> Mallory calls disablenetwork, calls sendmail as the first user after
> boot; sendmail can't deliver anything (its network is disabled), but
> starts forking and taking requests for other users, DoSing the mail
> delivery.

You need to be root to start sendmail as a daemon.  If Mallory is getting
a root shell before your /etc/rc.d scripts have started sendmail, you
have bigger problems.

> Scenario 3:
> 
> Mallory calls disablenetwork, then keeps hammering on su, knowing that
> su can no longer send data to audit subsystem and so he will not get caught.

I assume you mean syslog, not audit.  And it still won't work.

% strace /usr/bin/logger test message
...
socket(PF_FILE, SOCK_DGRAM|SOCK_CLOEXEC, 0) = 1
connect(1, {sa_family=AF_FILE, path="/dev/log"}, 110) = 0
sendto(1, "<13>Jan 11 21:49:25 logger: test"..., 40, MSG_NOSIGNAL, NULL, 0) = 40
close(1)                                = 0

su's complaint will get written to /dev/log which isn't interfered with
by the disablenetwork patch - and then syslogd will forward over the net
if configured to do so.

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